# How do the propeller blades accelerate air resulting in thrust to push an aircraft forward? [duplicate]

I do know that the blades on a propeller generate lift to provide a force pushing back on the air based on newton's law the 2nd. What I am having trouble understanding is how the blades generate thrust by cutting through the air? I know that helicopter hover because they push air downwards, but on a propeller the angle of the blades is much different than of a helicopters blades. Also I don't understand a zero lift configuration. I am having a lot of trouble understanding how helicopters push air downwards, as you can see in this picture

The airfoil doesn't look at all like it can push air downwards. I hope you guys can understand my confusion with this subject. Also I have looked this up on google and was provided answers that were way too confusing for me to understand, so can you give me an answer that is easy to understand. Thanks.

• Note that for a helicopter, the collective control changes the pitch of the rotor blades (kind of like a variable pitch prop on a fixed wing aircraft, but more complicated). Your image shows the blade pitch in a neutral position. – Greg Hewgill Sep 23 '15 at 2:45
• As @GregHewgill mentioned, the blades angle of attack is variable, what confuses you is that the image shows them in a neutral configuration that would not generate lift. The working angle is similar to what you can see on a fixed wing aircraft. Peter's answer and links clarify this. – mins Sep 23 '15 at 5:01

Propeller blades or rotor blades are like wings: They move through the air, and when they have the right angle of attack, they bend the air back- (in case of a propeller) or downwards (in case of the helicopter). On a wing, this causes downwash, on a propeller this causes prop blast. Both are really the same. Air gets a kick in a direction orthogonal to the movement of the airfoil, be it on a wing, a propeller or a rotor.

To make sure the angle of attack is right, a helicopter rotor uses a mechanism called collective pitch control to vary the angle of attack on all blades simultaneously. In addition, the rotor airfoil is carefully trimmed to have no chordwise shift in the center of pressure over angle of attack. Note that the rotor blade in the picture attached to your question has a small vane at the trailing edge: This is bent slightly upwards to trim the whole rotor such that it will not be twisted by aerodynamic loads.